1. Technical Field
The present disclosure relates to a liquid crystal display device, and more particularly, to a localized dimming method of a liquid crystal display device.
2. Discussion of Related Art
Demand for a high-performance display device that displays various kinds of information, such as images, graphics, and text has increased dramatically. Accordingly, display industries have shown rapid growth in recent years.
Thin film transistor (“TFT”) liquid crystal display (“LCD”) devices have been developed over the years to satisfy this demand. A TFT LCD device has low power consumption, is lightweight, thin, and does not release harmful electromagnetic waves as compared to a cathode ray tube (“CRT”) display device.
As compared to a plasma display panel (“PDP”) or the CRT display device, which are self emitting light devices, the TFT LCD device includes a TFT array, liquid crystals, and a backlight unit. The TFT array transfers an electric signal, the liquid crystals are rotated according to an applied voltage to transmit light, and the backlight unit is used as a light source at a rear side of the TFT LCD device.
A cold cathode fluorescent lamp (“CCFL”) can be used as the backlight unit of a TFT LCD device. The CCFL uses a cathode that does not emit heat and has low power consumption and high luminance.
A CCFL typically uses mercury. However, according to an environmental agreement, use of mercury is prohibited. Therefore, a backlight unit of a flat type that does not require mercury is needed.
A light emitting diode (“LED”) backlight unit can be used as a light source for the TFT LCD device, because the LED backlight unit does not use mercury, shows clear picture quality, and has wide color reproducibility for digital broadcasting.
When the LED backlight unit is used as the light source, a localized dimming operation that adjusts brightness of an LED per block according to image information can be implemented, thereby decreasing power consumption and enhancing a contrast ratio of an image.
FIG. 1 is a view showing a conventional LCD device using a CCFL, and FIG. 2A and FIG. 2B are views showing a principle of displaying an image of a conventional LCD device using a CCFL.
Referring to FIG. 1, an LCD device includes a display panel 102 and a backlight unit 101. The display panel 102 includes a TFT array substrate 103, a color filter array substrate 105, and liquid crystals (“LCs”) 107 interposed between the TFT array substrate 103 and the color filter array substrate 105. In the LCD device, the transmittance of light 109 transmitted from the backlight unit 101 is adjusted by an electric field applied to the TFT array substrate 103 and the color filter array substrate 105, thereby displaying an image.
The luminance of each pixel of the display panel 102 is determined by multiplying the illumination of the backlight unit 101 by the light transmittance of the LCs. In a conventional LCD device, an image with predetermined luminance is displayed by adjusting the transmittance of the LCs 107 after emitting the light 109 from the backlight unit 101 to the LCs by maximum illumination, as shown in FIG. 2A. However, since the light 109 provided to each pixel is more than necessary, power loss occurs.
A scaling system has been developed to reduce the power consumption. Referring to FIG. 2B, an image may be displayed even though the illumination of the backlight unit 101 is lowered below a maximum illumination. For example, the transmittance of the LCs in a pixel can be maximized by displaying an image having the brightest luminance and appropriately adjusting the transmittance of the LCs in the other pixels according to a ratio of the transmittance of the pixel displaying the image having the brightest luminance to the transmittance of the other pixels. The scaling system may reduce power consumption by lowering the illumination of the backlight unit 101.
FIG. 3 is a view showing a principle of displaying an image of a conventional LCD device using a localized dimming method. In the localized dimming method, the backlight unit 101 includes a plurality of blocks each having a light source and the illumination of the light source is individually adjusted. When the scaling system is applied to the localized dimming method, it is possible to maximize the transmittance of the LCs and to lower the illumination of the light source per block, thereby reducing the power consumption. When each block corresponds to a plurality of pixels, the transmittance of a pixel showing the brightest luminance is set to the maximum and the transmittance of the other pixels is adjusted by comparing the transmittance of the pixel showing the brightest luminance with the transmittance of the other pixels.
The localized dimming method can reduce the power consumption and improve a contrast ratio of the image. However, since an additional driving circuit per block is required to adjust the illumination of the light sources, manufacturing costs are increased.
Thus, there is a need for a backlight device for an LCD device, an LCD device, and a localized dimming method thereof, that can reduce manufacturing costs.